The amygdala is known to play a key role in perception, control over emotion, expression of anxiety and responding to threats.

But Menon and colleagues wanted to see how the amygdala developed from childhood to adulthood.

"We wanted to map out the developmental trajectory of these emotion-related circuits," says Menon.

He and colleagues used functional magnetic resonance imaging to study neuronal connections in the brain.

They compared the brains of 24 healthy children (aged 7 to 9) with that of 24 healthy adults (aged 19 to 22) who were lying passively in the scanner.

In particular, they were interested in two sub-units of the amygdala - the basolateral amygdala (BLA) and the centromedial amygdala (CMA) - which are known to play distinctly different roles in healthy adults.

The CMA controls the rapid expression of fear responses, such as freezing, while the BLA plays a critical role in our understanding of, and response to, emotional stimuli such as threats.

Cross talk

The researchers found that in the healthy adults, the CMA and BLA were distinct units, whose circuits were segregated, but this was not the case in children.

"In the children there was strong overlap between brain circuits that are supposed to be distinct," says Menon.

This could explain why children have such difficulty regulating emotions and are prone to tantrums. But the brain pattern is also seen in adults with anxiety.

"In adults with general anxiety disorder we've shown there is greater cross talk between these circuits," says Menon.

He says this network cross talk would make it harder for someone to evaluate a threat and make a calculated and reasoned response to it.

Therefore they might freeze or behave irrationally in response to fear, says Menon.

"The question is," he says. "At what age to these networks start to get segregated?"

The researchers suggest that reconfiguration of these networks may underlie the development of complex emotional responses during adolescence.